In order to increase a speed and to reduce power consumption in a semiconductor device, it is an important object to decrease the dielectric constant of an interlayer insulating film. Various designs have been made in order to decrease the dielectric constant. In a conventional semiconductor device, there have been proposed methods of:
(1) adding fluorine to a silica film to be an inorganic insulating film;
(2) forming an organic insulating material having a low dielectric constant as a host material; and
(3) intentionally forming a porous film.
In the method (1), however, the fluorine can be added in an element ratio of approximately several % at most because the heat resistance of the insulating film is deteriorated. For this reason, there is a problem in that a specific dielectric constant can be reduced by only 10% to 15% as compared with a conventional silica based interlayer insulating film.
In the method (2), moreover, a moisture resistance and a mechanical strength are deteriorated more remarkably as compared with the conventional silica based interlayer insulating film because of an organic material. Consequently, there is a problem in that the reliability of a semiconductor device is deteriorated.
In the method (3), furthermore, a porous structure is random. Therefore, the mechanical strength of an interlayer insulating film is remarkably reduced so that the interlayer insulating film is apt to be broken in packaging. For this reason, the reliability of the semiconductor device is deteriorated.
In many cases, moreover, the porous structure is not closed. If the porous structure is not closed, the moisture resistance of the interlayer insulating film is remarkably reduced so that the reliability of the semiconductor device is deteriorated.
With microfabrication and an increase in integration in a semiconductor device, furthermore, a capacity between wirings raises serious problems in addition to a capacity between wiring layers.
In the conventional insulating film, thus, a dielectric constant cannot fully be decreased. Moreover, there is a problem in that a mechanical strength cannot sufficiently be obtained.